In recent years, so-called Luxury Vinyl Tiles and Planks (LVT) have gained increasing success. These types of floor panels usually comprise a thermoplastic core, a thermoplastic décor layer arranged on the core, a protective layer on the décor layer, and a coating applied on the protective layer. The thermoplastic material is often PVC. The décor layer is printed with a pattern resembling natural stone, wood, ceramics etc. The pattern is often printed by rotogravure printing or direct printing. However, rotogravure printing or direct printing does not offer the desired flexibility in changing design of the patterns and adapting patterns for different needs of clients. Furthermore, a certain repetition of the pattern cannot be avoided by rotogravure printing or direct printing.
Recently, digital printing has offered new possibilities to the flooring industry to customize decorative patterns for flooring applications and to print small quantities of décor layers. By digital printing is conventionally meant printing by means of non-contact printing, for example using a Drop-on-Demand (DOD) technique. A drop of ink is placed with great accuracy on a paper or wood surface. Examples of DOD techniques are piezoelectric DOD inkjet and thermal DOD inkjet. In a piezoelectric DOD inkjet printer, the piezoelectric material changes shape when a voltage is applied. The change of shape of the piezoelectric material generates a pressure pulse in the fluid, thereby ejecting a droplet of ink from the nozzle. In a thermal DOD inkjet printer, ink drops are ejected by forming an ink vapour bubble by heating the ink.
Different kind of inks may be used for digital printing, such as UV curable inks, solvent based inks and aqueous inks (also called waterborne or water based inks). When printing on a thermoplastic surface such as a layer adapted to from a décor layer of a LVT, printing is facilitated by using UV curable inks or solvent based inks compared to aqueous inks. Printing with an aqueous ink on a thermoplastic surface has proved to be difficult. A drop of an aqueous ink does not stay but tends to bleed on the thermoplastic surface, resulting in a print of low quality. However, due to environmental reasons, it is favourable to replace UV curable inks and solvent based inks.
When the floor panel is assembled, the protective layer is bonded to the thermoplastic décor layer. It is thus important that the print does not affect the bonding between the layers adversely.